It is well known, in storm water and industrial liquid waste management systems, to provide ponds to receive contaminated water flows for treatment prior to discharging the treated water into local watersheds or sewers, where permitted. Treatment typically entails a first step of enabling fluid residence within the pond to allow for a time dependent, water quality improvement process to take place, such as sedimentation of suspended matter, including but not limited to silt, sand and clay. The initial residence step may include additional treatment or the additional treatment may be included in one or more subsequent steps, such as secondary and tertiary steps, to encourage composting, nutrient removal and the like for further clarifying the treated water.
In urban areas, municipal water ponds typically form a water feature about which residences may be located. Many of these constructed water bodies, particularly those in municipal settings, are of a size and configuration such that most of the pond surface area is within a fixed distance, for example about 50 m, of the pond's edge. Other ponds, such as industrial ponds or tailings ponds used in mining or oilsands processing or a variety of other industrial processes, are typically similarly sized. Further, the constructed water bodies may have components associated therewith from which much of the surface area of the pond is within the fixed distance. Over time, solid materials such as sediment may build up in these ponds, reducing the pond's utility. Applicant believes that the sediment which accumulates in these ponds tends to be of a uniform, slurry consistency. Accumulations of the sediment eventually reduce the ponds effectiveness.
A conventional remedy to pond sediment accumulation includes draining the pond in order to provide access for excavating machines and conveyance vehicles to remove and dispose of the sediment. One complication to such excavation processes is the close proximity of the residences, construction sites, landscaped terrains with trees or other valuable vegetation or other features which may surround the perimeter of the pond and restrict access thereto by the excavation equipment and sediment disposal carriers.
In municipal environments, remediation processes are often scheduled during the winter. The pond may be drained into the municipal sewer system if drainage onto natural water ways is not permitted during the winter months.
A plurality of backhoes is often employed in a chain arrangement to shovel sediment from a point in the pond to a point closer to the shore and from there to a point on shore for loading onto trucks. The process can, for example, take from 1 to 2 months for remediation of a typical storm water pond. Current cost estimated in Calgary, Alberta, Canada is about $3M for removal of sediment from each pond. Sediment removal is performed for each pond once every 10 to 20 years or so. Furthermore, Applicant believes that a current cost of disposing of the removed sediment is about $2M for each pond, particularly if special disposal procedures are required, such as for contaminated material landfill disposal as may be required for some stormwater or industrial water ponds. Thus, with a projected cost of about $5 million to remediate each stormpond, municipal governments are faced with significant budgeting issues. Given that large cities may have large numbers of stormponds and each stormpond will require remediation about every 10 to 20 years, the costs are significant.
The conventional remediation process, as described, is laborious, requires a long time to complete and is very expensive. Disposal of the drained water may be impractical due to government regulations and permits. Conventional pond remediation also tends to be disruptive to the peace and enjoyment of the local residents. Disposal of removed remediation materials, such as the sediment slurry, is expensive and impractical. Disposal typically involves a process of spreading slurry on other lands to allow the slurry to dry or thickening of the slurry using specialized dewatering equipment.
Shoreline and barge-mounted dredging has been exploited to remove materials from the bottom of water bodies as taught in U.S. Pat. No. 4,942,682 to McDowell. McDowell utilizes a self-contained, reversible dredging module adapted for use as an attachment to a conventional backhoe machine, thereby creating a two-segment backhoe. Applicant believes that access to the pond surface using such a two-segment backhoe is limited, such as to about 15 m from the shore.
As the surface of municipal ponds, industrial ponds or tailings ponds used in mining, oilsands and a variety of other industrial processes have a surface area typically extending much further than 15 m from the shore, a major portion of the pond surface is out of reach of the apparatus as taught in McDowell, unless the pond is almost completely dewatered or the apparatus is supported by a floating barge. Use of a floating barge sufficient in size to accommodate the apparatus of McDowell may be impractical, particularly for use in ponds where access is restricted such as in urban settings in close proximity to residences, construction sites, landscaped terrains and other types of access restrictions. McDowell does not disclose any sophisticated systems which might permit programming remediation patterns or monitoring the location of such apparatus relative to the pond surface and perimeter.
U.S. Pat. No. 4,911,831 to Davison et al teaches a self-propelled, floating apparatus and land-based crane gantry for skimming sand from beds of slow sand filters. An auger skimmer removes sand to a pre-determined depth and conveys the sand to a pump for delivery to a remote location via a floating conduit. The pump is located mid-point along the intake conduit away from the point of intake of the sand/water slurry. The slurry has a preferred density of 20% w/w sand. Augur depth is tracked and controlled however azimuthal location is not. Sonar, laser, audio and camera sensors are employed to set and monitor dredging depth. The apparatus of Davison et al is specifically designed for sand filter beds used in water purification plants and requires that weeds be removed from each filter prior to utilizing the sand skimmer. Cutters for removing weeds prior to suctioning the sand may be incorporated.
A floating, mechanical clamshell and hydraulic dredge is disclosed in U.S. Pat. No. 5,311,682 to Sturdivant. The dredge apparatus is fit with angular and linear displacement sensors to permit geo-location for data logging and quality assurance of work completed. Sturdivant is not shoreline based and must navigate the pond to each site requiring remediation. Sediment is removed at near in situ water content, as re-suspension due to water disturbance is minimized. High density sediment is removed and conveyed at low speed and may require pre-pump particle size reduction. A pipeline speed of 1 to 2 m/s compared to the prior art speeds of 2 to 5 m/s for a slurry density of 0% to 30% are quoted. Dredging operations may be tracked and optimized by electronically linking sensors on the apparatus to a data processor such as a PC or a PLC. Sensors on the apparatus may include GPS sensors.
An oil skimmer for use in remediation of oil spills is disclosed in published PCT application WO 2012/027620 to Brown et al. A platform or vehicle having an extendable arm is fit with a fluid skimmer for removing contaminants, particularly oil, which are at or near the surface of contaminated bodies of water such as rivers, lakes, marshes and the like. A pump on the skimmer collects contaminants from the water surface and delivers same to a collection reservoir, via a conduit. Alternatively, instead of a pump, a land-based service apparatus embodiment utilizes a boom connected directly to a vacuum truck for sucking water and contaminants from the surface of the water.
Systems and methods for improving water quality in ponds is described in Applicant's issued U.S. Pat. No. 8,333,895, incorporated herein by reference in it's entirety, with respect to Applicant's NAUTILUS POND®. The described systems focus on enhancing sediment and/or nutrient removal performance which are generally considered important functioning components of a pond system. Typically, removal of sediment accumulations from such ponds would require taking an entire pond offline for the duration of a sediment removal operation.
Land-based pond remediation, as disclosed in the prior art, appears to be limited largely by the reach of the equipment used, characteristics of the sediment slurry or other remediation material targeted for removal and pond operation. These limitations are exacerbated in developed areas due to additional constraints imposed by architectural features, landscaping and legislative considerations. Whereas these limitations may be overcome to some extent with the use of an improvised assortment of currently available equipment or a floating apparatus, the equipment is complex and adds constraints of transportation, provision of access to pond and adapted waste conveyance structures.
A remediation process, land-based or otherwise, is further complicated by the fact that prior art techniques require removal and disposal of sediment slurry to an offsite location. Transportation of the removed sediment slurry is inefficient as a large, majority fraction of the slurry volume, removed using prior art equipment is composed of water rather than solids. Use of specialized slurry thickening equipment may assist in reducing the water content and transportation costs, however the cost of each additional piece of equipment adds to the overall remediation operation cost, the complexity of the operations and the risk of equipment failure resulting in lengthy completion delays.
Clearly, there is interest in cost-effective, efficient, environmentally safe systems and methods for handling and storage of materials removed from water bodies such as ponds.